Hey we are currently in the MVP stage trying to find product market fit with a similar concept, but more focus on the illustrations: https://heytale.com
One major consideration we had with the pricing was comparing it to other providers. $19/month seems quite steep if you compare it to something like Disney Plus.
FYI List of some (likely not all) competitors in this space: https://topai.tools/s/Children's-story-generator https://theresanaiforthat.com/story-writing/